News Release Number: STScI-1997-25

World's Most Powerful Telescopes Team Up With a Lens in Nature to Discover Farthest Galaxy in the Universe

July 30, 1997: An international team of astronomers has discovered the most distant galaxy in the universe to date. They found it by combining the unique sharpness of the Hubble telescope with the light-collecting power of the W. M. Keck Telescopes— with an added boost from a gravitational lens in space.

The results show the young galaxy is as far as 13 billion light-years from Earth, based on an estimated age for the universe of approximately 14 billion years. The Hubble picture at left shows the young galaxy as a red crescent to the lower right of center. The galaxy's image is brightened, magnified, and smeared into this arc-shape by the gravitational influence of an intervening galaxy cluster, which acts like a gigantic lens. The image at upper right is a close-up of the "gravitationally lensed" galaxy. In the picture at lower right, astronomers have "unsmeared" the galaxy, revealing the galaxy's normal appearance.

Q & A: Understanding the Discovery

1.
What Was Discovered?

An international team of astronomers has discovered the most distant galaxy found in the universe to date.

2.
How Far Away Is It?

The galaxy is so far away that its light is only reaching us now from a time when the universe was but 7% of its current age of approximately 14 billion years. This places the young galaxy as far as 13 billion light-years from us, and far back in time during the "formative years" of galaxy birth and evolution.

3.
What Telescopes Were Used?

The team of astronomers made observations by combining the unique sharpness of the images from NASA's Hubble Space Telescope with the light-collecting power of the W. M. Keck Telescopes  and with an added boost from a gravitational lens in space.

5.
Why Do the Astronomers Consider the Discovery So Significant?

"When we received the Hubble image, we immediately knew that we had found something special," says Marijn Franx. "We were excited by the possibility that we may have found a unique example of a galaxy in formation at the time of the earliest quasars".

"We are fascinated to be witnessing the very early stages of the construction of what could well become a massive galaxy like our own Milky Way," says Garth Illingworth of University of California, Santa Cruz. "This object is a pathfinder for deciphering what is happening in young galaxies, and offers a rare glimpse of the powerful events that transpired during the formation of galaxies."

6.
What Does It Look Like?

Hubble shows that bright dense knots of massive stars power this object. Because of the firestorm of starbirth within it, the galaxy is intrinsically one of the brightest young galaxies in the universe, blazing with the brilliance of more than 10 times our own Milky Way. The object is similar to what Hubble sees in nearby starburst galaxies, though it is a very extreme and dramatic example.

7.
What Is a Gravitational Lens?

Predicted by Einstein's theory of general relativity gravitational lenses are collections of matter (such as clusters of galaxies) that are so massive they warp space in their vicinity, allowing the light of even more-distant objects to curve around the central lens-mass and be seen from Earth as magnified objects.

8.
Why Do Telescopes Need the Help of a Gravitational Lens?

The object is so far away, observing it in such detail would tax the capabilities of both Hubble and Keck without the magnification of the gravitational lens, provided by a foreground cluster of galaxies that is much closer to us at 5 billion light-years.

9.
How Did the Astronomers Know It Was a Lensed Object?

A telltale sign of the lensing is the fact the remote galaxy's image is smeared into an arc-shape by the gravitational influence of the intervening galaxy cluster. The smeared image of the galaxy stood out because of its unusual reddish color, never observed in such galaxies before.

10.
Why Is It Colored Red?

The special color of the galaxy in the arc is due to absorption by the matter in the universe between us and the galaxy, suggesting it was at a great distance.

11.
How Did the Astronomers Prove It's So Far Away?

The suspected remoteness of the lensed object was confirmed when the team of astronomers made spectroscopic observations with one of the twin Keck telescopes on Mauna Kea, Hawaii to measure its redshift (4.92), which is a measure of the expansion of space (due to the Big Bang) the larger the redshift, the greater space has expanded between us and the object. This can be used to estimate its distance.

12.
Haven't More Distant Objects Been Seen?

Though candidates for still more distant galaxies have been proposed, they have not been confirmed spectroscopically.

13.
What Does the Galaxy Really Look Like?

The researchers used a theoretical model of the effects of the gravitational lens to "unsmear" the galaxy back into its normal appearance. The corrected image clearly shows several bright, very compact regions of intense star formation.

14.
Why Are These Knots So Interesting?

The stellar knots could be the building blocks that eventually assembled to form the hub of a galaxy, like the central region of our Milky Way. The tiny, 700 light-year-sized stellar knots are scattered over a region that is only about 15,000 light-years across, only about a quarter the diameter of our Milky Way galaxy.

15.
What Do the Knots Tell Us About Early Galaxy Formation?

"Based on this image we can begin to make some conclusions about the early growth of galaxies," says Illingworth. "The knots show that starbirth happens in very tiny regions compared with the size of the final galaxy." This helps clarify the astronomer's view of the formation of galaxies as occurring within a cauldron of hot gas, with knots of intense star formation, strong winds, and "mergers"  collisions of the dense star-forming knots.

16.
What Else Has Been Learned?

Using Keck's spectroscopic capabilities, the astronomers have also, for the first time, been able to measure the motions of the gas within such a distant galaxy. The observations reveal a nearly half million mile per hour "wind"  an outflow of gas, presumably accelerated by energy from supernova explosions going off like a string of firecrackers.

17.
What Does the "Wind" Tell Us About Early Star Formation?

"The strong winds that we observe suggest that galaxies may lose a lot of material when they are young and thereby enrich the empty space around them," say Franx. "Many astronomers had speculated about the existence of such winds in such distant galaxies, and we now have an object where we can see them directly. It is striking that the most distant galaxy found to date is also the one that provides us the most detailed picture of events in such distant galaxies."